cgroup: factor out cgroup_apply_control_enable() from cgroup_subtree_control_write()

Factor out css enabling and showing into cgroup_apply_control_enable().

* Nest subsystem walk inside child walk.  The child walk will later be
  converted to subtree walk which is a bit more expensive.

* Instead of operating on the differential masks @css_enable, simply
  enable or show csses according to the current cgroup_control() and
  cgroup_ss_mask().  This leads to the same result and is simpler and
  more robust.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>

1 files changed, 47 insertions, 30 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 97cb1315bcac..1193038d0729 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3013,6 +3013,49 @@ static bool cgroup_drain_offline(struct cgroup *cgrp)
 }
 
 /**
+ * cgroup_apply_control_enable - enable or show csses according to control
+ * @cgrp: parent of the target cgroups
+ *
+ * Walk @cgrp's children and create new csses or make the existing ones
+ * visible.  A css is created invisible if it's being implicitly enabled
+ * through dependency.  An invisible css is made visible when the userland
+ * explicitly enables it.
+ *
+ * Returns 0 on success, -errno on failure.  On failure, csses which have
+ * been processed already aren't cleaned up.  The caller is responsible for
+ * cleaning up with cgroup_apply_control_disble().
+ */
+static int cgroup_apply_control_enable(struct cgroup *cgrp)
+{
+        struct cgroup *dsct;
+        struct cgroup_subsys *ss;
+        int ssid, ret;
+
+        cgroup_for_each_live_child(dsct, cgrp) {
+                for_each_subsys(ss, ssid) {
+                        struct cgroup_subsys_state *css = cgroup_css(dsct, ss);
+
+                        if (!(cgroup_ss_mask(dsct) & (1 << ss->id)))
+                                continue;
+
+                        if (!css) {
+                                css = css_create(dsct, ss);
+                                if (IS_ERR(css))
+                                        return PTR_ERR(css);
+                        }
+
+                        if (cgroup_control(dsct) & (1 << ss->id)) {
+                                ret = css_populate_dir(css, NULL);
+                                if (ret)
+                                        return ret;
+                        }
+                }
+        }
+
+        return 0;
+}
+
+/**
  * cgroup_apply_control_disable - kill or hide csses according to control
  * @cgrp: parent of the target cgroups
  *
@@ -3157,36 +3200,10 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
         cgrp->subtree_control = new_sc;
         cgrp->subtree_ss_mask = new_ss;
 
-        /*
-         * Create new csses or make the existing ones visible.  A css is
-         * created invisible if it's being implicitly enabled through
-         * dependency.  An invisible css is made visible when the userland
-         * explicitly enables it.
-         */
-        do_each_subsys_mask(ss, ssid, enable) {
-                cgroup_for_each_live_child(child, cgrp) {
-                        if (css_enable & (1 << ssid)) {
-                                struct cgroup_subsys_state *css;
-
-                                css = css_create(child, ss);
-                                if (IS_ERR(css)) {
-                                        ret = PTR_ERR(css);
-                                        goto err_undo_css;
-                                }
-
-                                if (cgrp->subtree_control & (1 << ssid)) {
-                                        ret = css_populate_dir(css, NULL);
-                                        if (ret)
-                                                goto err_undo_css;
-                                }
-                        } else {
-                                ret = css_populate_dir(cgroup_css(child, ss),
-                                                       NULL);
-                                if (ret)
-                                        goto err_undo_css;
-                        }
-                }
-        } while_each_subsys_mask();
+        /* prepare csses */
+        ret = cgroup_apply_control_enable(cgrp);
+        if (ret)
+                goto err_undo_css;
 
         /*
          * At this point, cgroup_e_css() results reflect the new csses